1. Technical Field
The present invention relates to a robot movement limiting method and apparatus, and to a robot apparatus equipped with the robot movement limiting apparatus.
2. Background Art
Robots, particularly those for industrial purposes, are widely used in automobile manufacturing factories and elsewhere. When the robots are operated, a robot arm and its wrist (together with a work or tools attached to the wrist) are instructed by a preset program stored in a control device to move along predetermined trajectories, such that they do not interfere with peripheral devices or travel wasteful distances. Further, a safety barrier is usually put up outside the aforementioned trajectories with a necessary margin such that no harm is ever inflicted to the operator, for example, by the movement of the arm or wrist of the robot.
The range of movement of a robot is also often controlled by a computer. For example, Patent Document 1 (JP Patent Publication (Kokai) No. 64-16395) discloses an industrial-robot control apparatus adapted to determine if the calculated transportation position of the arm tip (three-dimensional coordinate position of the robot) is included in a preset movement-prohibited region, at predetermined periods. If it is determined that the calculated position is within the preset range, the movement of the robot is ceased. Patent Document 2 (JP Patent Publication (Kokai) No. 8-108383) discloses a control apparatus whereby, in a robot equipped with an arm having a wrist joint, an envelope sphere is obtained that is created when the object that is being held is rotated about the wrist joint. Then, the presence or absence of contact with an obstacle as the envelope sphere is moved is determined and, if it is determined that a contact is probable, a new path is determined that would not result in the envelope sphere coming into contact with the obstacle.
By using the control methods disclosed in Patent Documents 1 and 2, the robot can be provided with alerting information before the work or tool mounted at the arm tip actually comes into the preset movement-prohibited region (obstacles), so that the robot can be operated more safely. These methods can protect the operator from harm or effectively prevent the incidence of the arm tip colliding with peripheral equipment when, particularly, the arm travels along trajectories other than those preset by the program, such as when the robot is being taught or upon program modification, or due to disturbance or noise.
Patent Document 1: JP Patent Publication (Kokai) No. 64-16395 A (1989)
Patent Document 2: JP Patent Publication (Kokai) No. 8-108383 A (1996)